82 research outputs found
High-spectral-resolution terahertz imaging with a quantum-cascade laser
We report on a high-spectral-resolution terahertz imaging system
operating with a multi-mode quantum-cascade laser (QCL), a fast scanning
mirror, and a sensitive Ge:Ga detector. By tuning the frequency of the QCL,
several spectra can be recorded in 1.5 s during the scan through a gas cell
filled with methanol (CH3OH). These experiments yield information about
the local absorption and the linewidth. Measurements with a faster frame
rate of up to 3 Hz allow for the dynamic observation of CH3OH gas leaking
from a terahertz-transparent tube into the evacuated cell. In addition to the
relative absorption, the local pressure is mapped by exploiting the effect of
pressure broadening
Broadband terahertz gas spectroscopy through multimode self-mixing in a quantum cascade laser
In the terahertz (THz) frequency range, CBRN agents and explosives have unique spectral signatures, which can be used for their identification and analysis. Quantum cascade lasers (QCLs) are important sources for spectroscopy within the 2–5 THz range, and self-mixing (SM) interference in a laser cavity enables the laser device to act both as a radiation source and as a coherent detector. This technique removes the need for additional detectors. Here, we present a SM spectroscopy technique, with an integrated frequency monitoring system and demonstrate the measurement of methanol spectral features simultaneously from two modes of a multi-mode THz QCL over a 17 GHz bandwidth
Characterization of coatings for straylight and photoluminescence suppression in the Raman Spectrometer for MMX (RAX)
The Martian Moons eXploration (MMX) mission led by JAXA to Mars moons Phobos and Deimos involves a small rover developed by DLR/CNES that will be operating on Phobos’ surface. Aboard it is the Raman Spectrometer for MMX (RAX), whose main scientific objectives address Phobos surface mineralogy, its heterogeneity and relation to the Mars mineralogy. Raman spectrometers require strong suppression of straylight, since this technique operates with few nano-Watt signals that should have significant contrast to all other sources of light inside the instrument. The mission requirements involving RAX call for a compact and sophisticated optical design, precluding space for straylight suppressive elements. To optimize straylight suppression in RAX, Raman scattering, Photoluminescence and reflection were characterized for candidate coatings representing different absorbing materials and fabrication technologies over spectral ranges between 530 nm and 680 nm. This was complimented by mechanical testing to aid selection of the coatings for parts inside the RAX flight model
Multi-spectral terahertz sensing: proposal for a coupled-cavity quantum cascade laser based optical feedback interferometer
We propose a laser feedback interferometer operating at multiple terahertz (THz) frequency bands by using a pulsed coupled-cavity THz quantum cascade laser (QCL) under optical feedback. A theoretical model that contains multi-mode reduced rate equations and thermal equations is presented, which captures the interplay between electro-optical, thermal, and feedback effects. By using the self-heating effect in both active and passive cavities, self-mixing signal responses at three different THz frequency bands are predicted. A multi-spectral laser feedback interferometry system based on such a coupled-cavity THz QCL will permit ultra-high-speed sensing and spectroscopic applications including material identification
Relevance of Phobos in-situ science for understanding asteroids
The origin of the martian moons, Phobos and Deimos is under debate since a very long time. There exist arguments and counter arguments that they may be captured asteroids. Other models favor, e.g., a massive impact at Mars as their origin [1]. The Martian Moons eXploration (MMX) mission by the Japan Aerospace Exploration Agency, JAXA, is going to explore both Martian moons remotely, but also return samples from Phobos, and deliver a small Rover to its surface [2,3]. This rover, provided by CNES and DLR, with contributions from INTA and the University of Tokyo has a payload of four scientific instruments, analyzing the physical, dynamical and mineralogical properties of Phobos´ surface. Parallels to asteroids of a similar size are eminent and the results will help deciphering the origin of Phobos [4]
OPTICAL DESIGN AND BREADBOARD OF THE RAMAN SPECTROMETER FOR MMX
This paper reports the laboratory confirmation of an optical design for a 0.2 numerical aperture confocal miniaturized, ruggedized Raman visible light spectroscope (RAX) to be borne by an autonomous rover landed on the martian moon, Phobos
In situ science on Phobos with the Raman spectrometer for MMX (RAX): preliminary design and feasibility of Raman meausrements
Mineralogy is the key to understanding the origin of Phobos and its position in the evolution of the Solar System. In situ Raman spectroscopy on Phobos is an important tool to achieve the scientifc objectives of the Martian Moons eXploration (MMX) mission, and maximize the scientifc merit of the sample return by characterizing the mineral composition and heterogeneity of the surface of Phobos. Conducting in situ Raman spectroscopy in the harsh environment of Phobos requires a very sensitive, compact, lightweight, and robust instrument that can be carried by the compact MMX rover. In this context, the Raman spectrometer for MMX (i.e., RAX) is currently under development via international collaboration between teams from Japan, Germany, and Spain. To demonstrate the capability of a compact Raman system such as RAX, we built an instrument that reproduces the optical performance of the fight model using commercial of-the-shelf parts. Using this performance model, we measured mineral samples relevant to Phobos and Mars, such as anhydrous silicates, carbonates, and hydrous minerals. Our measurements indicate that such minerals can be accurately identifed using a RAX-like Raman spectrometer. We demonstrated a spectral resolution of approximately 10 cm−1, high enough to resolve the strongest olivine Raman bands at ~820 and ~850 cm−1, with highly sensitive Raman peak measurements (e.g., signal-to-noise ratios up to 100). These results strongly suggest that the RAX instrument will be capable of determining the minerals expected on the surface of Phobos, adding valuable information to address the question of the moon’s origin, heterogeneity, and circum-Mars material transport
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